Radio aerial attachment



July 25, 1933-4 E. v. AMY ET Al.'

RADIO AERIAL ATTACHMENT Filed Aug. 10. 1932 Patented July 25, 1933 UNITED STATES PATENT OFFICE ERNEST V. AMY AND FRANK KING, 0F NEW YORK, N. Y., ASSIGNORS TO AMY, ACEVES & KING, INC., OF NEW YORK, N. Y., A CORPORATION 0F NEW YORK RADIO vAERIAL .ATTACHMENT Application mea August 1o, 1932. serial No. 628,142.

This invention relates to radio aerial attachments, and more particularly to a device for connecting a shielded downlead to an antenna or other aerial and comprising a matching impedance transformer.

In the use of radio broadcast receiving sets much annoyance is caused by noise due to interference by local electrical equipment, such as electrical refrigerators, door bells, elevator motors, etc. Mostly such linterference from such man made static is due to electrical disturbances induced in the downlead from the aerial to the receiving set. Disturbances induced in the aerial can be prevented only by changing the construction or location of the aerial, but' the downlead conductors may be and are commonly protected against picking up such electrostatic interference by providing the conductor with a metallic shield insulated from it and grounded, the shield usually being a metallic Woven or other flexible tubing covering the insulated conductor. y

Such shielded downlead conductors, while they serve well to eliminate electrostatic interference from local sources, have the disadvantage that they cause a large loss in the signal energy reaching the receiving? set, this being due to the large capacity between the conductor and the shield as compared to the capacity of the aerial. The effective ca'- lpacity of a shielded conductor 75 feet long is from l0. to 30 times as great as thatof the average receiving aerial or antenna. The capacitive reactance of a shielded downlead conductor is therefore small in comparison to that of the antenna, and, consequently, a considerable amount of energy is wasted and the power delivered through the downlead from the aerial is far from the maximum possible. In many cases, because ofl the desirability of having the antenna set so as to avoid inductive disturbance from local sources, and because of other conditions, the receiving set is positioned at a considerable distance from the aerial; and because of the necessarily long shielded downlead the signal strength is greatly diminished. Even with a comparatively short shielded downlead there is a very considerable loss.

This loss, resulting 'from the use of a shielded downlead, has been overcome by connecting an impedance matching trans-l former between the shielded downlead and the aerial, and this makes it possible to have the aerial positionedv so as in most cases to avoid disturbances induced in the -aerial from local sources, with the result that full strength operation of the set may be secured without interference from man made. static even under severe conditions of proximate electrostatic disturbance. It has been demonstrated that when so connected to the aerial, a receiving set will operate with very nearly the same signal `strength when positioned 'as much as 300 feet from the antenna as when substantially directly connected therewith and free of metallic shielding. ff

The present invention vaims to provide a device for connecting a shielded downlead to an aerial with an impedance matching transformer between the downlead' and the aerial which may be quickly and conveniently attached directly to the aerial or to a lead therefrom at any desired point therealong. A further object of the invention is to provide such a device which is adapted to add to the electrical pick-up characteristie of the aerial.

To these ends, the invention in the preferred embodimentv comprises an impedance matching transformer mounted within a housing formed by a metal shell open at the bottom and a bottom closure of insulating material, and having a connecting member extending from the top of the casing formed for attachment to and for making electrical connection with the aerial, and provided with means for connecting the transformer to the downlead conductor and to ground. Such' an embodiment of the invention is lillustrated in the accompanying drawing, in which Fig. 1 is a view in elevation showing an installation including the downlead connecting device of the invention;

Fig. 2 is a sectional view on a larger scale of the connecting device Fig. 3 is a, detail sectional view taken on line 3-3 of Fig. 2;

Fig. 4 is a circuit diagram showing the electric circuits of the devlce as shown in Fig. 2; and

` Figs. 5 and 6 are circuit diagrams illusvtra'ting alternative arrangements.

Referring to the drawing, Fig. 1 shows a typical installation in Awhich the downlead connecting device T, which provides an impedance matching transformer connected between the aerial and the receiving' set, is shown as suspendedy from an antenna aerial A and having connected to it a shielded downlead conductor S leading to a radio` receivingset indicated at R. The shielded conductor comprises an insulated conducting wire or cable s which as shown is covered by a shield s of woven wire or other iiexible tubing. Both the conductor s and the shield s are connected to the transformer of the device T, and at the set end the conductor s is connected to the antenna terminal a of the receiving set, and from the shield s and the ground terminal g of the set a suitable ground connection is made as by a conductor g connected to a water pipe w.

The downlead connecting device T as shown in Fig. 2 comprises an impedance matching transformer 10 within a casing formed by a metal shell 11 which is most desirably bell-shaped open at the bottom, and a bottom closing disc 12 of hard fiber sheet, the edge of the shell being shouldered and crimped over the edge of the disc. The transformer should, of course, be one suitable to serve the intended purpose of at least substantially reducing the difference between the impedance of the shielded downlead and that of the aerial. It should, therefore, be a step-down transformer in the direction from the aerial to the downlead, and for best results the impedance of its primary should substantially match the impedance of the aerial, and the impedance of its secondary should match substantially the impedance of the downlead conductor, and it should give maximum coupling. Because of its simple construction and the closel coupling which it a'ords, we have found a suitable auto-transformer with multi-layer winding most desirable. Transformers of other forms might, however, be used.

Fig. 2 shows a simple form of a multi-layer auto-transformer consisting of a coil 15 wound on a bobbin formed by two dished fiber discs 16 and a spacing ring 17, the discs being held together by a centrally set eyelet 18. This transformer is mounted on the disc 12 and is held in place by a screw bolt 20 which extends through a central opening in the disc 12 and through a bushing 21 and the eyelet 18 to receive a nut 22 which when tightened on the bolt draws a iiange 23 on the bolt against the outside of the disc 12.

The bolt 20 is connected by a terminal 24 and a lead 25 to an intermediate point of the coil 15, and the head 26 of the bolt extending from the outer side of the disc 12 is formed to serve as a connecting member for securing the end of the downlead conductor. The downlead conductor is thus connected through disc 12 to. the secondary tap of the transformer coil.

The lead 30 from one end of the coil 15 is connected to a terminal 31 held by a nut 32 on a screw 33 which extends through an openin in the top of the shell 11 and the head o which is formed to provide a connecting member for attaching the device T to the aerial. The lead 40 from the other end of the coil 15 has connected thereto and extending out through an eyelet in the disc 12 a conductor 41 which serves as a connecting member for making a ground connection, usually by connection with the downlead shield as shown in Fig. 1. The portion of the coil between the secondary ta and the lead 40 serves as, and may be re erred to as, the secondary of the transformer in addition to being part of the primary.

.The construction of the connecting member by which the downlead connecting device is attached to the aerial will depend on the form of the aerial. This connecting member of the device shown by Figs. 1 to 3 is intended for attaching the device to an antenna wire, or to a wire leading from the antenna or other aerial. In the construction shown, the head 34 of the terminal screw 33 is made with a Hat face and has a tapped hole to receive a clamping screw 35 and has a transverse slot 36. A washer 37 serves to clamp the antenna Wire against the flat side of the head when the screw is tightened with the device positioned so that the antenna wire lies along the slot. The connecting device may thus conveniently be attached directly to the antenna or other wire so that the device will be suspended therefrom and electrically connected thereto. Connecting members. of other construction will be provided for devices which are to be attached to other forms of aerials.

The device desirably has within the casing means providing a safety gap, or lightning arrester, connected across the transformer and the connection to the downlead conductor.- For this purpose, a short fiber tube 50 is screwed on t0 the end of the terminal screw 33 and has in its other end a screw 51. The ends of the screws 33 and 51 are suitably pointed and spaced to provide a gap of the desired length, and connection is made from a terminal held by the screw 51 through an extension of the lead 40 to the ground connecting conductor 41, thus providing a normally open short-circuiting safety-gap connection from the antenna to Sliy 4tage of this downlead connecting device is` the ground shunting the transformer and the connection to the downlead conductor.

The space within-the casin is desirably filled with wax or other suita le insulating filling material. This serves the usual purpose of protecting the transformer coil against the condensation of moisture and gives added assurance against short circuit- Fig. 4 shows conventionally the electrical wiring of the device shown in Figs. l and 2. The ground connection Gr will usually be made through the shield of the downlead conductor as shown in Fig. 1 when the downlead cable has a'shield which is a good conductor. Otherwise, as when usin a leadshielded cable, a separate grounding cable should be used, and this may be the second conductor which is commonly provided inl the lead-sheathed cables used as shielded downleads. If, .instead of an auto-transformer, the device is rovided with a twocoil transformer, the wlring connections may be as represented by Fig. 5. Fig. 6 shows an arrangement in which the antenna is connected through the transformer coil to a counterpoise. In this case a second ground connection will be required from the secondary coil or secondary port-ion of the coil of' the transformer, and this will necessitate, as indicated by the diagram, a third connection from the transformer through the bottom disc of the connecting device casing.

The device of the'invention'whereby an impedance matching transformer and a shielded downlead may be attached directly to an antenna or other aerial or connecting wire leading therefrom has, as willbe seen, important advantages. The installation of the device is extremely simple, economical and practical. It is self-supporting and avoids the necessity of using any brackets or supporting structures for' mounting the transformer to any wall, pipe or other such support, and electrical losses due to faulty insulation under adverse weather conditions or otherwise are greatly reduced. The device may be connected at any point along the length of an antenna. For certain types of long aerials this is a distinct advantage for obtaining the best pick-up of a particular desired wave length. A further advanthat the metal shell of the casing adds substantially in some cases to the electrical pickup obtained from the aerial. For a short antenna of say 20 to 25 feet in length the added electrical pick-up by the metal shell of this device will usually give a noticeable improvement in the signal strength obtained, the improvement depending on the surface area of the shell, which `may Vary from a few inches to a square foot or more.

The terms aerial and antenna as used in the claims are to be construed as transformer with Ithe shielded downlead i conductor and with ground.

2. The combination with a radio receiving aerial and a shielded downlead, of a device for connecting the downlead to the aerial comprising connecting means suspending .the device from and making electrical connection to the aerial, and impedance matching transformer connected with said connecting means, and means connecting the transformer with. the downlead conductor and the downlead shield.

3. A device for connecting a shielded downlead to a radio receiving aerial, comprising an impedance matching transformer, means for connecting the transformer with the downlead conductor and with ground, and a connecting member whereby the device may be suspended from the aerial and the transformer electrically connected thereto.

4. A device for connecting a shielded downlead to a radio receiving aerial, comprising a casing formed by a metal shell open at the bottom and a bottom closure of insulating material, a connecting member extendin from the top of the casing and formed or attachment to and for making electrical connection with the aerial, connecting members extending from thebottom closure for connection to the downlead conductor and the downlead shield respectively, and an impedance matching transformer within the casing connected between the aerial connecting member and the downlead connecting members. l

5. A device for connecting a jshielded downlead to a radio receiving antenna, comprising a casing having a bell-shaped metal member extending from the top of the casing formed for attachment to and for making electrical connection with the aerial, an

impedance matching transformer formed by a coil wound on a flat bobbin mounted flatwise on said bottom disk and secured by a bolt passing through the bottom disk and centrally through the bobbin and having an outside head formed to serve as a connecting member for the shielded downlead conductor, and a connection from said bolt to an intermediate point of the coil, one end of the transformer coil being electrically connected with the top connecting member and the other end of the coil having a ground connection extending through said disk.

7. A devicefor connecting a shielded downlead to a radio receiving aerial, comprising a casing having a bottom closing disk of insulating material, a connectmg member formed for attachment to and for making electrical connection with the aerialv and having a screw stud which extends through the top of the casing and is held by an inside nut, an impedance matching transformer mounted on said disk and secured by a bolt passing through the bottom disk and electrically connected to a secondary lead of the transformer and having an outside head formed to serve as a connecting member for the shielded downlead conductor, a short tube of insulating material one end of which is screwed on to said screw stud, a gap terminal in the other end of said tube, the ends of said terminal and said screw stud being shaped and spaced to form a safety gap, one primary lead of the transformer being electrically connected with said top connecting member, and a ground connection extending through said disk and connected to the other primary lead and to said gap terminal.

8. A device for connecting a shielded downlead to a radio receiving aerial, comv prising an encased impedance matching transformer, means for connecting the transformer at different points to the downlead conductor and downlead shield respectively of a shielded downlead, and means for suspending the unit from the aerial and for making electrical connection between the aerial and the transformer.

9. A device for connecting a shielded downlead to a radio receiving aerial, comprising an encased impedance matching transformer, means for connecting the transformer at different oints to the downlead conductor and down ead shield respectively of a shielded downlead, and means, comprising a post rigid with said casing and having a clamp,for suspending the unit from the aerial and for making electrical connection between'the aerial and the transformer.

10. A device for connecting a shielded downlead to a radio receiving aerial, comprising an impedance matching transformer, a casing within which the transformer is mounted,-means including a post projecting from the lower part of the casing and a wire lead for connecting the transformer at different points to the downlead conductor and downlead shield respectively of a shielded downlead, and means, comprising a post rigid with and electrically connected to said casing, for suspending the unit from the aerial and for making electrical connection between the aerial and the transformer. A

11. In a device of the character described, a housing comprising a metal shell and a bottom of insulating material, an impedance matching transformer fixed Within said housing and electrically connected to said metal shell, a binding post projecting from the' top of said metal shell in electrical connection therewith, a binding post depending from said bottom in electrical connection with said transformer and having a shank and locking means for securing the transformer to said bottom, and a lead from said utransformer extending through said bottom to make electrical connection with the shield of a shielded downlead when the downlead conductor is attached to the bottom binding post.

12. In a device of the character described, a housing comprising a metal shell and a bottom of insulating material, an impedance matching transformer fixed within said housing and electrically connected to said metal shell, a binding post projecting from the top of said metal shell in electrical connection therewith, a binding post depending from said -bottom in electrical connection with said transformer and having a shank and locking means for securing the transformer to the bottom, and a lead from said transformer extending through said bottom to make electrical connection with the shield of a shielded downlead when the downlead conductor is attached to the bottom binding post, the post on said metal shell having a portion within the housing carrying spaced conductors the lower one of which is in connection with said lead.

13. In a device of the character described, a housing comprising a metal shell and a bottom of insulating material, a substantially flat impedance matching transformer on said bottom within the housing, a post extending centrally through and fixed to said bottom having locking means for securing the transformer on the bottom and a projection with terminal clamp outside the housing, a post extending centrally through and fixed to and in electrical connection with said shell and having a clamp outside the housing and spaced conductors inside prollO Viding a safety gap, connections from said transformer to the bottom post and to the shell post, and a lead from said transformer through 'said bottom for connection to the `shield of a shielded downlead connected to the bottom post, said lead having a connection with one of said spaced conductors.

14. The combination with a radio receiving aerial and a shielded downlead, of a device for connecting the downlead to the aerial comprising a casing, means for Suspending the casing from the aerial, an impedance matching transformer Within the casing, connecting means for connectinor the primary of the transformer to the aerial` and the primary and secondary of the trans-v former to ground, and means for connecting the secondary of the transformer to the downlead conductor.

15. The combination with a radio receiving aerial and a shielded downlead, of a ERNEST V.- AMY. FRANK KING. 

